Bidirectional differential valve

ABSTRACT

An automatic control system for use with a hydraulic drive system which includes a source of pressurized hydraulic fluid and first and second hydraulic drive motors deriving their power from said source of pressurized hydraulic fluid, comprising a differential valve in fluid communication with the source of pressurized hydraulic fluid and a flow divider in fluid communication with the differential valve and with a flow compensator. The flow compensator is in fluid communication with the first and second hydraulic drive means. A compensator valve member is carried by the flow compensator for controlling the relative rates of flow of hydraulic fluid to the first and second hydraulic drive motors in response to load variations encountered by the hydraulic drive means. A control unit is in fluid communication with the source of pressurized hydraulic fluid and with the flow divider and includes a control valve member for controlling hydraulic fluid signals being sent therefrom to the flow divider. An actuator is operatively connected to the control valve member for actuating the control valve member in response to stimulus from a source external to the automatic control system. A flow divider valve member is carried by the flow divider for controlling the relative rates of flow of hydraulic fluid through the flow divider in response to the hydraulic fluid signals from the control unit.

United States Patent 119 Allen BIDIRECTIONAL DIFFERENTIAL VALVE Thomas E. Allen, Mustang, Okla.

CMl Corporation, Oklahoma City, Okla.

Filed: June 8, 1973 Appl. No.: 368,105

Related US. Application Data Division of Ser. No. 266,505, June 26, 1972, Pat. No. 3,774,40l.

Inventor:

Assignee:

US. Cl. 137/112, 137/1 is Int. Cl. G05d 1/00 Field of Search 137/112, 118; 60/97 E [56] References Cited A UNITED STATES PATENTS 6/1966 Thompson 137/112'x- 12/1967 9/1971 Primary Examiner-William R. Cline Attorney, Agent, or Firm-Dunlap, Laney, l-lessin, Dougherty & Codding 57 ABSTRACT An automatic control system for use with a hydraulic Weisenbach 60/97 E Shore l37/ll2 June 11, 1974 drive system which includes a source of pressurized hydraulic fluid and first and second hydraulic drive motors deriving their power from said source of 'pres surized hydraulic fluid, comprising a differential valve in fluid communication with the source of pressurized hydraulic fluid and a flow divider in fluid communication with the differential valve and with a flow compensator. The flow compensator is in fluid communication with the first and second hydraulic drive means. A compensator valve member is carried by the flow compensator for controlling the relative rates of flow of hydraulic fluid to the first and second hydraulic drive motors in response to load variations encountered by the hydraulic drive means. A control unit is in fluid communication with the source of pressurized hydraulic 'fluid and with the flow divider and includes .a control valve member for controlling hydraulic fluid signals being sent therefrom to the flow divider. An

2 Claims, 10 Drawing Figures l BIDIRECTIONAL DIFFERENTIAL VALVE BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates generally to automatic control systems for use with hydraulic drive systems, and more specifically, but not by way of limitation, to automatic control systems for use with heavy construction machinery such as paving machines or the like.

2. Brief Description of the Prior Art Known examples of the prior art teach various systems for automatically controlling hydraulic drive systems. Certain of these systems employ complex and expensive mechanically and electrically actuated valving to provide a desired degree of control; Many prior art systems have not been entirely satisfactory due to the expense involved in both the manufacture and maintenance of various component parts thereof. Others of the prior art systems have not been entirely satisfactory due to delay in response of the drive system to the control signals sent thereto by the automatic control systern, and due to wander or oscillation inherent in the automatic control system.

SUMMARY OF THE INVENTION The present invention contemplates an improved automatic control system for use with a hydraulic drive system of the type which includes a source of pressurized hydraulic fluid and first and second hydraulic drive means deriving their power from said source of pressurized hydraulic fluid. The automatic control system comprises differential valve means, having an inlet in fluid communication with the source of pressurized hydraulic fluid and having an outlet, for providing a hydraulic pressure differential between the inlet and outlet thereof. A flow divider having first and second signal inlets, a power inlet, and first and second power outlets communicates with the outlet of the differential valve means via the power inlet thereof. A flow compensator, having first and second power inlets and first and second power outlets, is connectedto the flow divider via the first and second power inlets thereof in fluid communication with the first and second power outlets of the flow divider, respectively. The flow compensator is further in fluid communication with the first and second hydraulic drive means by means of the first and second power outlets, respectively, thereof. Compensator valve means is carried by said flow compensator between the first power inlet and the first power outlet, and between the second power inlet and the second power outlet thereof for controlling the relative rates of flow of hydraulic fluid to said first and second hydraulic drive means from said flow compensator in response to load variations encountered by said first and second hydraulic drive means. A first control unit having an inlet in fluid communication with the source of pressurized hydaulic fluid and having first and second signal outlets is in fluid communication with the first and second signal inlets of the flow divider by means of the first and second signal outlets thereof, respectively. First control valve means is carried by the first control unit between the inlet thereof and the first and second signal outlets thereof for controlling the relative rates of flow of hydraulic fluid through the first and second signal outlets of the first control unit to the first and second signal inlets of the flow divider, respectively. First actuation means is operatively connected to the first control valve means for actuating the first control valve means in response to stimulus from a source external to the automatic control system. Flow divider valve means is carried by the flow divider between the power inlet thereof and the first and second power outlets thereof, and in fluid communication with the first and second signal inlets thereof for controlling the relative rates of flow of hydraulic fluid from the power inlet to the first power outlet and from the power inlet to the second power outlet in response to the rela tive flow rates of hydraulic fluid from the first control unit into the first and second signal inlets of the flow divider.

An object of the present invention is to provide an improved automatic control system for use with a hydraulic drive system which will automatically compensate for deviation of the hydraulic drive system from desired path. I

Another object of the present invention is to provide an improved automatic control system for use with a hydraulic drive system which will automatically compensate for variations in the loads encountered by the individual hydraulic drive motors of the hydraulic drive system.

Yet another object of the present invention is to pro-.

BRIEFDESCRIPTION OF THE DRAWINGS FIG. 1 is a substantially diagrammatical perspective view illustrating the apparatus of the present invention installed on a hydraulically driven self-propelled vehicle.

FIG. 2 is a schematic diagram illustrating onev form of the automatic control system of the present invention.

FIG. 3 is a cross-sectional view of one form of flow divider for use with the present invention illustrating the details of construction thereof.

FIG. 4 is a cross-sectional view of one form of flow compensator for use with the present invention illustrating the details of construction thereof.

FIG. 5 is a schematic diagram illustrating anothe form of the automatic control system of the present invention.

FIG. 6 is a cross-sectional view of another form of flow divider for use with the present invention illustrat ing the details of construction thereof.

FIG. 7 is a cross-sectional view of another form of flow compensator for use with the present invention il lustrating the details of construction thereof. FIG. 8 is a cross-sectional view of one form of bidirectional differential valve for use with the present invention illustrating the details of construction thereof.

FIG. 9 is a cross-sectional view of the valve of FIG. 8 showing the disposition of the valve member when the pump is driven in the forward direction.

FIG. 10 is a cross-sectional view of the valve of FIG. 8 showing the. disposition of thevalve member when the pump is driven in the reverse direction.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, and to FIG. 1 in particular, the apparatus of the present invention is generally designated by the reference character 10. The apparatus 10 includes a self-propelled vehicle 12 comprising a frame 14 and four hydraulic motor-driven track units 16 positioned at each of the four corners of the frame 14 and supporting the frame 14 on the ground.

While the vehicle 12 is described herein to include four hydraulic motor-driven track units 16, it will be readily understood that the present invention is equally well suited for use with vehicles having two drive units disposed respectively on opposite sides of the vehicle.

Mounted on and supported by the frame 14 is .an automatic control assembly 18. Details of the construction of the automatic control assembly 18 will be described in greater detail hereinafter.

A track drive pump 20 is mounted onthe frame 14 and is connected to the automatic control assembly 18 by means of a pair of hydraulic conduits 22 and 24. The track drive pump 20 is driven by a power take-off which is driven by a suitable engine such as an internal combustion engine'of the piston or turbine type (not shown). A hydraulic fluid reservoir 26 is mounted on the frame 14 and is in fluid communication with the track drive pump 20 by means of a hydraulic conduit 28. A hydraulic fluid filter 30 is interposed in the con duit 28 between the track drive pump 20 and the hydraulic fluid reservoir 26. In certain applications, alternate or additional filters may be desirable.

Hydraulic track drive motors 32, 34, 36 and 38 are mounted respectively on and drivingly connected to the hydraulic motor-driven track units 16. The first port 32a of the track drive motor 32 is in fluid communication with the automatic control assembly 18 via hydraulic conduits 40 and 42. The second port 32b of the track drive motor 32 is in fluid communication with the automatic control assembly via hydraulic conduits 44 and 46. The first port 34a of track drive motor 34 is in fluid communication with the automatic control assembly 18 via hydraulic conduits 40 and 48. The second port 34b of track drive motor 34 is in fluid communication with the automatic control assembly 18 via hydraulic conduits 50 and 44.

It should be noted that it may be desirable in certain circumstances to include a conventional flow divider at the junction of conduits 42 and 48 to divide the flow of hydraulic fluid therethrough from conduit 40. Similarly, it may also be desirable to include a second conventional flow divider at the junction of conduits 60 a and 54 to, divide the flow of hydraulic fluid therethrough from conduit 52. In addition, a conventional flow divider may also be included at the junctions of conduits 46 and 50 to divide the flow of hydraulic fluid therethrough from conduit 44. Similarly, it may also be desirable to include a conventional flow divider at the junction of conduits 62 and 58 to divide the flow of hydividers may suitably be of the 50 -50 type which is well known to those skilled in the art.

The first port 36a of track drive motor 36 is in fluid communication with the automatic control assembly 18 via hydraulic conduits 52 and 54. The second port 36b of track drive motor 36 is in fluid communication with the automaticcontrol assembly 18 via hydraulic conduits 56and 58. The first port 38a of track drive motor 38 is in fluid communication with the automatic control assembly 18 via hydraulic conduits 52 and 60. The second port 38b of track drive motor 38 is in fluid communication with the automatic control assembly 18 via hydraulic conduits 56 and 62.

A hydraulic manual steering control assembly 64 is mounted 'on the frarne'l4 and is in fluid communication with the automatic-control assembly 18 via hydraulic supply conduit 66 and hydraulic signal conduits 68 and 70.

A sensor control assembly 72 is mounted on and to one side of the frame 14. The sensor control assembly 72 is in fluid communication with the automatic control assembly 18 via hydraulic supply conduit 74 and hydraulic signal conduits 76 and 78. The sensor control assembly 72 includes a sensor unit 80 operatively connected thereto by means which will be described in greater detail hereinater. Each sensor unit 80is provided with a tracer 82 which engages a string line or grade line 84 which is supported above the surface of the ground to provide a suitable reference datum to facilitate the automatic steering of the apparatus 10. A shut-off valve 86 is installedin the hydraulic supply conduit 74 intermediate the sensor control assembly 72 and the automatic control assembly 18 to provide means for manually deactivating the sensor control assembly 72 when desired.

The sensor control assembly 72 is preferably mounted on the vehicle 12 proximate the forward end thereof when the vehicle 12 is moving in the forward direction. Conversely, the sensor control assembly 72 is preferably mounted on the vehicle 12 proximate the rear end thereof when the vehicle 12 is moving in the reverse direction.

A heat exchanger 88 is mounted on the frame 14 and is in fluid communication with the'hydraulic fluid reservoir 26 via conduit 90. The bypass outlet 92 of the track drive motor 32 is in fluid communication with the heat exchanger 88 via hydraulic conduits 94, 96 and 98. The bypass outlet 100 of the track drive motor 34 is in fluid communication with the heat exchanger 88 via hydraulic conduits 102, 96 and-98. The bypass outlet 104 of the track drive motor 36 is in fluid communication with the heat exchanger 88 via hydraulic conduits 106, 108 and 98. The bypass outlet 110 of the track drive motor 38 is in fluid communication with the heat exchanger88 via hydraulic conduits 112, 108 and 98. The track drive motors 32, 34, 36 and 38 are adapted, by means of their internal valving, to direct excess fluid volume through the respective bypass outlets .92, 100, 104 and 110 through the associated hydraulic conduits to the heat exchanger 88. At the heat exchanger 88 the excess hydraulic fluid is cooled and directed from the heat exchanger 88 through hydraulic conduit 90 to the hydraulic fluid reservoir 26 for re-use in the hydraulic drive system of the apparatus 10.

It will be readily apparent to those skilled in the art that the apparatus 10 may be propelled over the ground by means of the four hydraulic motor-driven track units 16 which are driven respectively by the track drive motors 32, 34, 36 and 38, which track drive motors derive their power from the flow of hydraulic fluid emanating from the track drive pump 20 and conveyed thereto through the previously described hydraulic conduits and the automatic control assembly 18. Control of the relative speed and power outputs of the track drive motors 32, 34, 36 and 38 is achieved by the automatic control assembly 18 interposed between the track drive pump 20 and the track drive motors. Preferred embodiments of the automatic control assembly 18 will be described in detail hereinafter.

DESCRIPTION OF THE EMBODIMENT OF FIGS. 2, 3 AND 4 FIG. 2 generally illustrates, in schematic form, the automatic control assembly 18 in fluidcommunication with the hydraulic manual steering control assembly 64, the sensor control assembly 72, the shut-off valve 86, and the track drive motors 32 and 38 as described in detail above. The track drive motors 34 and 36 are not illustrated in FIG. 2, it being believed that it will be readily apparent to one skilled in the art that the operation of the motors 34 and 36 is substantially'identical to the operation of motors 32 and 38 which will be described in detail herein. FIG. 2also illustrates the track drive pump 20 in fluid communication with the auto matic control assembly 18 as described above.

The automatic control assembly 18 includes a differential valve 114. The inlet 116 of the differential valve 114 is in fluid communication with the first port 20a of the track drive pump 20 via hydraulic conduits 118 and 22.

The automatic control assembly 18 also includes a flow divider 120 having first and second signal inlets 122 and 124, a power inlet 126 and first and second power outlets 128 and 130. The power inlet 126 of the flow divider 120 is in fluid communication with the outlet 132 of the differential valve 114 via conduit 134.

A shuttle valve 136 having an outlet 138 is in fluid communication with the first signal inlet 122 of the flow divider 120 via conduit 140. A second shuttle valve 142 having an outlet 144 is in fluid communication with the second signal inlet 124 of the flow divider 120 via conduit 146.

The shuttle valve 136 also includes a first inlet 148 and a second inlet 150. The first inlet 148 is in fluid communication with the sensor control assembly 72 via conduits 152 and 76. The second inlet 150 is in fluid communication with the hydraulic manual steering control assembly 64 via conduits 154,156 and 68.

The second shuttle valve 142 includes a first inlet 158 and a second inlet 160. The first inlet 158 is in fluid communication with the sensor control assembly 72 via conduits 162 and 78. The second inlet 160 is in fluid communication with the hydraulic manual steering control assembly 64 via conduits 164, 166 and 70.

The second inlet 150 of the shuttle valve 136 is also in fluid communication with the power inlet 126 of the flow divider 120 via conduits 154, 168 and 134. An orifree 170 is interposed in conduit 168 intermediate conduits 154 and 134. The second inlet 160 of the shuttle valve 142 is also in fluid communication with the power inlet 126 of the flow divider 120 via conduits 164, 172 and 134. An orifice 174 is interposed in the conduit 172 intermediate the conduits 164 and 134.

The automatic control assembly 18 further includes a flow compensator 176. The flow compensator 176 includes first and second power inlets 178 and 180, and first and second power outlets 182 and 184. The first and second power inlets 178 and are in fluid com munication with the first and second power outlets 128 and 130 of the flow divider 120, respectively.

Included in the automatic control assembly 18 is a forward-reverse control valve 186. The valve 186 includes an inlet port 188, a forward outlet port and a reverse outlet port 192. The inlet port 188 is in fluid communication with the first port 20a of the track drive pump 20 via conduits 194, 196, 118 and 22. The valve 186 is illustrated in the forward mode with the inlet port 188 and the forward outlet port 190 in fluid communication with one another. It will be readily apparent that the valve 186 may be placed in the reverse mode by placing the inlet port 188 in fluid communication with the reverse outlet port 192 by moving the control lever 198 in the direction indicated by the arrow 200 to the reverse position.

The automatic control assembly 18 further includes a pair of forward-reverse spool valves 202 and 204. The spool valve 202 includes power ports 206, 208, 210 and 212. The spool valve 202 also includes a pair of control ports 214 and 216.

The spool valve 204 includes power ports 218, 220, 222 and 224. The spool valve 204 also includes a pair of control ports 226 and 228.

The forward outlet port 190 of the forward-reverse control valve 186 is in fluid communication with the control port 214'of spool valve 202 via conduits 230 and 232. The forward outlet port 190 is also in fluid communication with the control port 226 of spool valve 204 via conduits 230 and 234. The reverse outlet port 192 of the forward-reverse control valve 186 is in fluid communication with the control port 216 of spool valve 202 via conduits 236 and 238. The reverse outlet pport 192 is also in fluid communication with the control port 228 of spool valve 204 via conduits 236 and 240.

The first power outlet 182 of the flow compensator 176 is in fluid communication with the power port 206 of spool valve 202 via conduit 242. The second power outlet 184 of the flow compensator 176 is in fluid communication with power port 218 of the spool valve 204 via conduit 244.

The power port 208 of spool valve 202 is in fluid communication with the second port 20b of the track drive pump 20 via conduits 246, 248 and 24. The power port 220 of spool valve 204 is in fluid communication with the second port 20b of the track drive pump 20 via conduits 250, 248 and 24. The power port 210 of spool valve 202 is in fluid communication with the track drive motor 32 via conduits 252, 40 and 42. The power port 212 of spool valve 202 is in fluid communication with the track drive motor 32 via conduits 254, 44 and 46. The power port 222 of spool valve 204 is in fluid communication with the track drive motor 38 via conduits 256, 52 and 60. The power port 224 of spool valve 204 is in fluid communication with the track drive motor 38 via conduits 258, 56 and 62.

The hydraulic manual steering control assembly 64 preferably includes a conventional hydraulic differential flow control valve 260 having an inlet port 262 and a pair of signal outlet ports 264 and 266. The valve 260 may be suitably actuated by a manually operated control lever or the like as shown at 268. The inlet port 262 of the control valve 260 is in fluid communication with the automatic control assembly 18 and the first port 20a of the track drive pump 20 via conduits 66, 196, 118 and 22. The signal outlet 264 is in fluid communication with conduit 68 and the signal outlet 266 is in fluid communication with the conduit 70.

The sensor control assembly 72 includes a conventional hydraulic differential flow control valve 270 having an inlet port 272 and a pair of signal outlet ports 274 and 276. The signal outlet port 274is in fluid communication with conduit 76 and the signal outlet port 276 is in fluid communication with conduit 78. The

'inlet port 272 is in fluid communication with the automatic control assembly 18 and the track drive pump 20 via conduits 74, 278, 118 and 22. As described above, a shut-off valve 86 is installed in the conduit 74 intermediate the inlet port 272 of the sensor control assembly 72 and the automatic control assembly 18. The hydraulic differential flow control valve 270 is of conventional construction and its operation will be readily apparent to those skilled in the art.

The sensor unit 80 is operatively connected to the hydraulic differential flow control valve 270 of the sensor control assembly 72 in order to actuate the valve 270 in response to variation in the position of the sensor unit 80 relative to the string line or grade line 84. The sensor unit 80 may be directly connected to the valve 270 by mechanical means or may be connected electrically to the valve 270 to provide actuation thereof. Such sensor units are well known in the art and need not be described in detail herein.

The valves 260 and 270 are commonly referred to as selector or directional control valves. The valve 260 is preferably of the low gain type while the valve 270 is preferably of the high gain type. In each of the valves 260 and 270 the cross-sectional flow area to one or the other signal outlet ports is directly proportional to the input signal from the control lever 268 or the sensor unit 80, respectively.

As shown in FIG. 3, the flow divider 120 comprises a valve body 280 and a valve member 282 slidably disposed therein. The valve body 280 includes a bore 284 extending therethrough and intersecting the opposite end portions 286 and 288 thereof. A counterbore 290 is formed in the bore 284 intersecting the end portion 286 and forming an annular wall 292 in the valve body 280. A counterbore 294 is formed in the bore 284 intersecting the opposite end portion 2880f the valve body 280 and forming an annular wall 296 therein.

A central annular chamber 298 is formed in the medial portion of the valve body 280 and includes opposite annular walls 300 and 302 interconnected by a cylindrically shaped annular surface 304. The annular chamber 298 is coaxial with the bore 284.

Asecond annular chamber 306 is formed in the valve body 280 coaxial with the bore 284 and intermediate the counterbore 280 and the central annular chamber 298. The annular chamber 306 includes opposite annular walls 308 and 310 interconnected by a cylindrically shaped annular surface 312.

A third annular chamber 314 is formed in the valve body 280 coaxial with the bore 284 therethrough and intermediate the central annular chamber 298 and the counterbore 294. The annular chamber 314 includes opposite annular walls 316 and 318 interconnected by a cylindrically shaped annular surface 320.

The first signal inlet 122 of the flow divider 120 communicates with an annular chamber 322 formed by the counterbore 290. The second signal inlet 124 of the flow divider 120 communicates with an annular chamber 324 formed by the counterbore 294. The power inlet 126 of the flow divider 120 communicates with the central annular chamber 298. The first and second power outlets 128 and 130 of the flow divider 120 communicate with the annular chambers 306 and 314, respectively.

The valve member 282 is slidably disposed in the bore 284 of the valve body 280. The substantially cylindrically shaped outer periphery 326 of the valve member 282 has a diameter sized to provide a substantially fluid-tight seal between the outer periphery 326 and the walls of the bore 284. A cylindrically shaped extension 328 is formed on one end portion 329 of the valve member 282 and extends into the annular chamber 324. The extension 328 is coaxial'with the outer periphery 326 of the valve member 282. An annular shoulder 330 interconnects the cylindrical surface 332 of the extension 328 and the cylindrically shaped outer periphery 326.

A bore 334 is formed in the cylindrically shaped extension 328 coaxial with the cylindrical surface 332. A counterbore 336 is formed in the valve member 282 intersecting the end portion 338 thereof and communicating with the bore 334 in the extension 328. A removable orifice 340 is threadedly securedin the end portion 342 of the extension 328. A plug 344 having an aperture 346 formed therein is threadedly secured in the counterbore 336 at the end portion 338 of the valve member 282. A removable orifice 348 is threadedly secured in the aperture 346.

Two ports 350 are formed in the valve member 282 providing communication between the chamber 352 formed therein by the counterbore 336 and the central annular chamber 298 in the valve body 280.

A plurality of ports 354 are formed in the valve member 282 proximate to the end portion 338 thereof. The ports 354 provide fluid communication between the chamber 352 and the cylindrically shaped outer periphery 326 of the valve member 282. Similarly, a plurality of ports 356 are formed in the valve member 282 proximate to the end portion 329 thereof. The ports 356 provide fluid communication between the chamber 352 and the cylindrically shaped outer periphery 326 of the valve member 282. Preferably, the valve member 282 includes ten ports 354 and ten ports 356. The diameters of the ports 354 and 356 are preferably identifive ports on the other side diametrically opposed thereto. The ports 354 and 356 are drilled or otherwise formed in the valve member 282 on centers substantially equal to the diameter of the ports. It should also be noted that the centers of the five ports 354 and 356 on one side of the valve member 282 are preferably staggered approximately one-half the diameter of a port from the centers of the ports 354 and 356, respectively, formed in the opposite side of the valve member 282. The staggered relation of the ports 354 and 356 provides smooth transition as the valve member 282 moves left or right within the valve body 280. It should be noted that the arrangement and/or diameter of the ports 354 and 356 may be varied to achieve other than linear flow response to movement of the valve member 282 within .the valve body 280. It should further be noted that other forms of ports such as long slots may 'be substituted for the previously described pluralityof ports 354 and 356.

, As shown in FIG. 3, the valve member 282 is positioned in its center or medial position within the valve body 280. In this position, it will be observed that five ports 354 communicate between the chamber 352 of the valve member 282 and the annular chamber 306 of the valve body 280. Similarly, five ports 356 provide communication between the chamber 352 of the valve member 282 and the annular chamber 314 of the valve body 280. The remaining ports 354 and 356 are blocked by the cylindrical walls of the bore 284 and therefore provide no communication between the chamber 352 and the chambers 306 and 314.

As will be readily apparent to those skilled in the art, as the valve member 282 moves either left or right of the central or medial position the cross-sectional area of the ports 354 and 356 providing fluid communication between the chamber 352 and the cylindrically shaped outer periphery 326 of the valve member 282 always remains equal to the total cross-sectional area of ten ports.

The valve member 282 is urged into its central or medial position relative to the valve body 280 as shown in FIG. 3, by means of a spring assembly 358 disposed within the chamber 324 formed by the counterbore 294 in the valve body 280. The spring assembly comprises two identical annular spring seats 360 and 362. Each spring seat 360 and 362 has a cylindrically shaped aperture 364 formed therein and is L-shaped in crosssection with an outwardly extending flange portion 366 and a cylindrically shaped portion 368. An annular end wall370 is formed on each flange portion 366.

The spring seat 360 is slidably disposed on the cylindrically shaped extension 328 with the extension 328 extending through the aperture 364 formed therein. The end wall 370 thereof abuts the annular shoulder 330 of the valve member 282 and also abuts the annular wall 296 of the valve body 280 when the valve member 282 is positioned in its central or medial position. The annular spring seat 362 is slidably disposed on the cylindrically shaped extension 328 with the extension 328 extending through the aperture-364 therein and with the end wall 370 thereof facing away from the annular spring seat 360. The annular spring seats 360 and 362 are retained on the cylindrically shaped extension 328 by means of a snap ring 372 disposed in an annular groove 374 formed in the cylindrical surface 332 of the extension 328.

The spring assembly 358 further includes a coil spring 376 disposed about the cylindrically shaped ex-' tension 328. The coil spring 376 is supported at each end thereof by the respective cylindrically shaped portion 368 of the respective annular spring seat 360 and i l0 threaded cap screws 388. A suitable fluid-tight seal is provided between the end plates 384 and 386 and the valve body 280 by means of O-rings 390 disposed in annular grooves 392 formed in'the end plates 384 and 386.

The second end face 382 of the annular sleeve 378 abuts the end plate 386. Movement of the valve member 282 within the valve body 280 is yieldably resisted by the urging of the coil spring 376. Movement of the valve member 282 to the right, as viewed in FIG. 3, is resisted by the urging of the coil spring 376 acting through the end plate 386, the annular sleeve 378, the spring seat 362, the coil spring 376, the spring seat 360, and the annular shoulder 330 of the valve member 282.

Movement of the valve member 282 to the left, as 1 viewed in FIG. 3, is resisted by the urging of the coil valve body 280, the spring seat 360, the coil spring 376, the spring seat 362, the snap ring 372, and the cylindrically shaped extension 328 of the valve member 282.

As shown in FIG. 4, the flow compensator 176 comprises a valve body 394 and a valve member 396 slidably disposed therein. The valve body 394 includes a bore 398 extending therethrough and intersecting the opposite end portions 400 and 402 thereof. A counterbore 404 is formed in the bore 398 intersecting the end portion 402 and forming an annular wall 406 in the valve body 394.

A first annular chamber 408 is formed in the valve body 394 and includes opposite annular walls 410 and 412 interconnected by a cylindrically shaped annular surface 414. The annular chamber 408 is coaxial with the bore 398.

A second annular chamber 416 is formed in the valve body 394 coaxial with the bore 398. The annular chamber 416 includes opposite and annular walls 418 and 420 interconnected by a cylindrically shaped annular surface 422.

The first power inlet 178 of the flow compensator 176 communicates with the first annular chamber 408. The second power inlet 180 of the flow compensator 176 communicates with the second annular chamber 416.

A third annular chamber 424 is formed in the valve body 394 coaxial with the bore 398- therethrough and intermediate the first annular chamber 408 and the end portion 400 of the valve body 394. The annular chamber 424 includes opposite annular walls 426 and 428 interconnected by a cylindrically shaped annular surface 430.

A fourth annular chamber 432 is formed in the valve body 394 coaxial with the bore 398 therethrough and intermediate the second annular chamber 416 and the end portion 402 of the valve body 394. The annular chamber 432 includes opposite annular walls 434 and 436 interconnected by a cylindrically shaped annular surface 438.

The first power outlet 182 of the flow compensator 176 communicates with the third annular chamber 424; and the second power outlet 184 of the flow compensator 176 communicates with the fourth annular chamber 432.

The valve member 396 is slidably disposed in the bore 398 of the valve body 394. The cylindrically shaped outer periphery440 of the valve member 396 has a diameter sized to provide a substantially fluid- 11 tight seal between the outer periphery 440 and the walls of the bore 398. The valve member 396 includes opposite end faces 442 and 444, each lying in a plane normal to the longitudinal axis of the valve member 396. A cylindrically shaped chamber 446 is fonned in one end of the valve member 396 with one end thereof intersecting the end face 442. A second cylindrically shaped chamber 448 is formed in the opposite end of the valve member 396 with one end thereof intersecting the end faces 444. It should be noted that the chambers 446 and 448 do not communicate with each other within the valve member 396.

Two ports 450 are formed in the valve member 396 providing communication between the chamber 446 formed therein and the first annular chamber 408 formed in the valve body 394. Two ports 452 are formed in the valve member 396 providing communication between the chamber 448 formed therein and the second annular chamber 416 formed in the valve body 394. Two ports 454 are formed in the valve member 396 providing communication between the chamber 446 formed therein and the third annular chamber 424 formed in the valve body 394. Two ports 456 are formed in the valve member 396 providing communication between the chamber 448 formed therein and the fourth annular chamber 432 formed in the valve body 394.

As shown in FIG. 4, the member 396 is positioned in its center or medial position within the valve body 394. It will be observed that the centerline of the ports 454 and the centerline of the ports 456 are positioned substantially in the planes of the annular walls 426 and 436 of the third and fourth annular chambers 424 and 432, respectively.

End plates 458 and 460 are secured respectively to the opposite end portions 400 and 402 of the valve body 394 by suitable means such as a plurality of threaded cap screws 462. A suitable fluid-tight seal is provided between the end plates 458 and 460 and the valve body 394 by means of O-rings 464 disposed in annular grooves 466 fonned in the end plates 458 and 460.

. The valve member 396 is of such length that when it is displaced to the extreme left, as viewed in FIG. 4, with the end face 442 thereof abutting the end plate 458, the cross-sectional area of fluid communication between the chamber 446 of the valve member 396 and the third annular chamber 424 of the valve body 394 via the ports 454 is closed off entirely. At the same time, the communication between the chamber 448 and the valve member 396 with the fourth annular chamber 432 of the valve body 394 via the ports 456 is at a maximum. Alternately, when the valve member 396 is displaced to the extreme right, as viewed in FIG. 4, with the end face 444 thereof abutting the end plate 460, the cross-sectional area of fluid communication between the chamber 448 of the valve member 396 with the fourth annular chamber 432 of the valve body 394 is closed off entirely. At the same time, communication between the chamber 446 of the valve member 396 withthe third annular chamber 424 of the valve body 394 via the ports 454 is at 'a maximum. It should be noted that regardless of the relative position of the valve member 396 within the valve body 394 the communication between the chamber 446 of the valve munication between the chamber 448 of the valve member 396 and the second annular chamber 416 of the valve body 394 via the ports 452 remains unchanged regardless of the position of the valve member 396 relative to the valve body 394.

It should be noted that the previously described flow divider and flow compensator 176 may be advantageously housed in a single unitary valve body. Such a valve body would include all of the features described for the valve bodies 280 and 394 of the flow divider 120 and flow compensator 176, respectively, and would place the first and second power outlets 128 and 130 of the flow divider 120 in fluid communication with the first and second power inlets 178 and 180, respectively, of the flow compensator 176 within the combined valve body. Furthermore, the end plates 458 and 384 may be advantageously combined into one end plate as may end plates 460 and 386. In either configuration the functions of the flow divider 120 and the flow compensator 176 would be identical.

OPERATION OF THE EMBODIMENT OF FIGS. 2, 3 AND 4 In operation, the track drive pump 20 is driven by the engine and power take-off (not shown) to provide a source of pressurized hydraulic fluid. The pressurized hydraulic fluid provided by the pump 20 may be in either a low pressure range of from 600 to 1,500 psi or in a high pressure range of from 1,500 to 3,500 psi. While these pressure ranges are disclosed as preferable for the operation of the present invention, it is not intended that the present invention be limited thereby.

The pressurized hydraulic fluid is directed from the first port 200 of the pump 20 through conduits 22 and 118 to the inlet 116 of the differential valve 114. The hydraulic fluid passes through the differential valve 114 and exits from the outlet 132 theereof. The differential valve 114 provides a pressure differential of approximately 75 psi between the high pressure inlet 116 and the lower pressure outlet 132. The hydraulic fluid is then directed from the outlet 132 through conduit 134 to the power inlet 126 of the flow divider 120.

Pressurized hydraulic fluid is also directed from the pump 20 via conduits 22, 118, 278 and 74 to the inlet port 272 of the sensor control assembly 72. In order for the pressurized hydraulic fluid to reach the inlet port 272 of the sensor control assembly 72 it is necessary for the shut-off valve 86, installed in conduit 7.4, to be in its open position. If the shut-off valve 86 is in the closed position the sensor control assembly 72 is deactivated and performs no function in the operation of the present invention. The pressurized hydraulic fluid flows from the inlet port 272 through the differential flow control valve 270 of the sensor control assembly 72 and exits therefrom through the signal outlet ports 274 and 276. The hydraulic fluid emanating from the signal outlet port 274 flows to the first inlet 148 of shuttle valve 136 via conduits 76 and 152. The hydraulic fluid emanating from the signal outlet port 276 flows to the first inlet 158 of shuttle valve 142 via conduits 78 and 162.

Pressurized hydraulic fluid also flows from the pump 20 to the inlet port 262 of the hydraulic differential flow control valve 260 of the hydraulic manual steering control assembly 64 via conduits 22, 118, 196 and 66. The hydraulic fluid entering the inlet port 262 passes through the hydraulic differential flow control valve I 260 and exits therefrom through signal outlets 264 and 266. A portion of the hydraulic fluid emanating from the signal outlet 264 flows to the second inlet 150 of the shuttle valve 136 via conduits 68, 156 and 154. The remaining portion of the hydraulic fluid emanating from the signal outlet 264 flows to the power inlet 126 of the flow divider 120 via conduits 68, 156, 168 and 134. It should be noted that the last-mentioned hydraulic fluid must also pass through orifice 170 in conduit 168. The passage of the hydraulic fluid through the orifice 170 provides the pressure drop required in order for the hydraulic fluid to reach the lowered pressure of the hydraulic fluid emanating from the outlet 132 of the differential valve 114.

A portion of the hydraulic fluid emanating from the signal outlet 266 flows to the second inlet 160 of the shuttle valve 142 via conduits 70, 166 and 164. The remaining portion of the hydraulic fluid emanating from the signal outlet 266 flows to the power inlet 126 of the flow divider 120 via conduits 70, 166, 172 and 134. It should be noted that this hydraulic fluid must also pass through orifice 174 in the conduit 172 which provides the necessary pressure drop for the hydraulic fluid to reach the lower pressure of the hydraulic fluid emanating from the outlet 132 of the differential valve 114.

Pressurized hydraulic fluid entering either of the inlets 148 or 1500f the shuttle valve 136 exits therefrom through outlet 138 and flows to the first signal inlet 122 of the flow divider 120 via conduit 140. Pressurized hydraulic fluid entering either of the inlets 158 or 160 of the shuttle valve 142 exits therefrom through outlet 144 and flows to the second signal inlet 124 of the flow divider 120 via conduit 146.

The hydraulic fluid entering the power inlet 126 of the flow divider 120 passes through the power inlet 126 into the chamber 352 in the valve member 282 via the central annular chamber 298 of the valve body 280 and the ports 350 formed in the valve member 282. The hydraulic fluid entering the first signal inlet 122 of the flow divider 120 flows into the annular chamber 322 of the valve body 280 through the first signal inlet 122, and then flows from the annular chamber 322 into the chamber 352 of the valve member 282 through the orifice 348. The hydraulic fluid entering the second signal inlet 124 of the flow divider 120 flows into the annular chamber 324 of the valve body 280 through the second signal inlet 124, and then flows from the annular chamber 324 into the chamber 352 of the valve member 282 through the orifice 340 and the bore 334 of the extension 328.

It should be noted that the hydraulic fluid inthe annular chambers 322 and 324 is at a pressure approximately 75 psigreater than the hydraulic fluid contained within the chamber 352 of the valve member 282. As the hydraulic fluid enters the annular chambers 322 and 324 flows into the chamber 352 through the respective orifices 348 and 340 the pressure drops to that of the hydraulic fluid within the chamber 352 of the valve member 282.

The hydraulic fluid in the chamber 352 of the valve member 282 flows therefrom through the ports 354 and 356 into the second and third annular chambers 306 and 314 of the valve body 280, respectively. The hydraulic fluid entering the second annular chamber 306 through the ports 354 exits therefrom through. the first power outlet 128; and the hydraulic fluid entering the third annular chamber 314 through the ports 356 exits therefrom through the second power outlet 130. The hydraulic fluid exiting from the first power outlet 128 of the flow divider flows therefrom intothe first power inlet 178 of the flow compensator 176. The hydraulic fluid exiting from the second power outlet 130 of the flow divider 120 flows therefrom into the second power inlet of the flow compensator 176.

Orifices 170, 174, 340 and 348 can be sized to provide various steering rates in response to manual and sensor signal inputs. I

The hydraulic fluid entering the first power inlet 178 of the flow compensator 176 flows therefrom into the chamber 446 of the valve member 396 through the first annular chamber 408 of the valve body 394 and the ports 450 of the valve member 396. The hydraulic fluid entering the second power inlet 180 of the flow compensator 176 flows therefrom into the chamber 448 formed in the valve member 396 through the second annular chamber 416 of the valve body 394 and-the ports 452 formed in the valve member 396. The hydraulic fluid in the chamber 446 of the valve member 396 flows therefrom through the ports 454 formed in the valve member 396 and the third annular chamber 424 of the valve body 394 and exits from the flow compensator 176 through the first power outlet 182. The hydraulic fluid in the chamber 448 of the valve member 396 flows therefrom through the ports 456 in the valve member 396 and the fourth annular chamber 432 of the valve body 394 and exits from the'flow compensator 176 through the second power outlet 184.

The hydraulic fluid exiting from the first power outlet 182 of the flow compensator 176 flows therefrom to the power port 206 of the forward-reverse spool valve 202 via conduit 242. The hydraulic fluid exiting from the second power outlet 184 of the flow compensator 176 flows therefrom to the power port 218 of the for ward-reverse, spool valve 204 via conduit 244. When the forward-reverse spool valves 202 and 204 are in their forward positions, the hydraulic fluid entering power port 206 of spool valve 202 exits therefrom through power port 210, and the hydraulic fluid entering the power port 218 of spool valve 204 exits therefrom through power port 222. p

The hydraulic fluid exiting from power port 210 of spool valve 202 flows therefrom through conduits 252, 40 and 42 to track drive motor 32 thereby driving the motor 32 in a forward direction. Most of the hydraulic fluid passing through the track drive motor 32 is routed therefrom back to the power port 212 of the spool valve 202 via conduits 44, 46 and 254. Excess hydrau-. lic fluid volume bypassed by the internal valving of the track drive motor 32 is directed from bypass outlet 92 through conduits 94,96 and 98 to heat exchanger 88 and from heat exchanger 88 through conduit 90 to reservoir 26.

Hydraulic fluid exiting from power port 222 of spool valve 204 flows therefrom through conduits 256, 52 and 60 to track drive motor 38 thereby driving the motor 38 in a forward direction. Most of the hydraulic fluid passing through track drive motor 38 is routed therefrom back to power port 224 of spool valve 204 via conduits 56, 62 and 258. Excess hydraulic fluid volume bypassed by the internal valving oftrack drive motor 38 is directed from bypass outlet 110 through conduits 108, 112 and 98 to heat exchanger 88 and from heat exchanger 88 through conduit 90 to reservoir 26.

Hydraulic fluid entering power port 212 of spool valve 202, when spool valve 202 is in the forward position, exits therefrom through power port 208 and flows back to track drive pump via conduits 246, 248 and 24. Similarly, when spool valve 204 is in the forward position hydraulic fluid entering power port 224 exits therefrom through power port 220 and flows back to the track drive pump 20 via conduits 250, 248 and 24.

To place the forward-reverse spool valves 202 and 204 in the proper forward or reverse positions, hydraulic fluid is directed from the first port 20a of the pump 20 through the forward-reverse control valve 186 to the appropriate control ports of the spool valves 202 and 204. Pressurized hydraulic fluid flows to the inlet port 188 of the forward-reverse control valve 186 from the pump 20 via conduits 22, 118, 196 and 194. When the forward-reverse control valve 186 is in the forward position, as shown in FIG. 2, the hydraulic fluid entering the inlet port 188 flows through the valve 186 and exits from the forward outlet port 190. The hydraulic fluid exiting from the forward outlet port 190 communicates with the control ports 214 and 226 of the spool valves 202 and 204, respectively. Fluid communication between the forward outlet port 190 and control port 214 of spool valve 202 is'accomplished via conduits 230 and 232; and fluid communication between the forward outlet port 190 and the control port 226 of spool valve 204 is accomplished via conduits 230 and 234.

When the forward-reverse control valve 186 is placed in the reverse position by moving the control lever 198 in the direction of the arrow 200, the pressurized hydraulic fluid entering inlet port 188 of the valve 186 exits therefrom through reverse outlet port 192. Thereverse outlet port 192 is in fluid communication with control ports 216 and 228 of spool valves 202 and 204, respectively. The pressurized hydraulic fluid emanating from reverse outlet port 192 communicates with control port 216 via conduits 236 and 238 thereby placing spool valve 202 in the reverse position. The hydraulic fluid emanating from reverse outlet port 192 also communicates with control port 228 of spool valve 204 via conduits 236 and 240 thereby placing spool valve 204 in the reverse position. Y

At this point it should be noted that, while a single forward-reverse control valve 186 is disclosed for simultaneously controlling the forward-reverse spool valves 202 and 204, it will be understood that it may be preferable to control the spool valves 202 and 204 individually by separate forward-reverse control valves similar to the previously described valve 186. in addition, the spool valves 202 and 204 may be individually controlled by separate mechanical means such as manually operated levers directly connected to the valves 202 and 204, respectively. Such individual control of the spool valves 202 and 204 will permit one spool valve to be placed in the reverse mode while the other spool valve is simultaneously placed in the forward mode thereby permitting the vehicle 12 to make spot turns to the left or the right about a vertical axis.

When forward-reverse spool valve 202 is in the reverse position, hydraulic fluid entering the valve 202 through power port 206 exits the valve 202 through power port 212 and flows to the track drive motor 32 via conduits 254, 44 and 46 thereby driving the track drive motor 32 in the reverse direction. Most of the hydraulic fluid passing through track drive motor 32 flows therefrom through conduits 40, 42 and 252 to power port 210 of spool valve 202. The hydraulic fluid entering power port 210 passes through spool valve 202 and exits from power port 208 to return to the second port 20b of the pump 20 via conduits 246, 248 and 24.

When forward-reverse spool valve 204 is in the reverse position, hydraulic fluid entering port 218 of the spool valve 204 exits therefrom through power port 224 and flows through conduits 258, 56 and 62 to track drive motor 38 thereby driving track drive motor 38 in the reverse direction. Most of the hydraulic fluid passing track drive motor 38 flows therefrom through conduits 52, 60 and 256 to power port 222 of spool valve 204. Hydraulic fluid entering power port 222 passes through spool valve 204 and exits from power port 220 to return to the second port 20b of the pump 20 via conduits 250, 248'and 24.

When track drive motors 32 and 38 are driven in the reverse direction, excess hydraulic fluid volume by passed by the internal valving of the track drive motors 32 and 38 is directed from bypass outlets 92 and 100, respectively, back to the reservoir 26 as previously described in detail for the forward operation of the track drive motors 32'and 38.

It will be readily apparent to those skilled in the art that the valving described for providing the reversing of the flow of hydraulic fluid to the track drive motors 32 and 38 may be actuated in any number of well-known ways. One such way would be bythe application of direct mechanical force to the valves 202 and 204 either in substitution for the hydraulic actuation means previously described, or as a back-up actuation system in addition to the hydraulic actuation system. Another suitable actuation means would be the utilization of electric solenoids for actuation of the valves 202 and 204.

Automatic control of the output of track drive motors 32 and 38 is accomplished by properly setting the sensor control assembly .72 such that the tracer 82 will properly engage the string-line or grade-line 84 to provide actuation of the hydraulic differential flow control valve 270. When the sensor control assembly 72 is properly adjusted onthe apparatus 10, as illustrated in FIG. 1, the shut-off valve 86 is placed in the open position to permit the flow of pressurized hydraulic fluid from the pump 20 through conduits 22, 118, 278 and 74 to the inlet port 272 of the hydraulic differential flow control valve 270.

The forward-reverse control valve 186 is placed in the forrward position thereby causing the spool valves 202 and 204 to be placed in the forward position when the pump 20 is driven by the engine through the power take-off, as shown in FIG. 2. When the apparatus 10 is in proper alignment with the string line 84, as sensed by the sensor control assembly 72, pressurized hydraulic fluid from the pump 20 passes through the appropriate conduits through the differential valve 114 and into the flow divider where the hydraulic fluid entering power inlet 126 thereof is equally divided and emanates from the flowdivider 120through the first and second power outlets 1'28 and in streams having substantially equal flow rates. The hydraulic fluid emanating from the power outlets 128 and 130 enters the flow compensator 176 through the first and second power inlets 178 and 180 thereof, respectively. Assuming that the loads encountered by track drive motors 32 and 38 are equal, the separate streams of hydraulic fluid entering the first and second power inlets 178 and 180 exit the first and second power outlets 182 and 184, respectively, of the flow compensator 176 at equal flow rates. The hydraulic fluid emanating from the first power outlet 182 flows through appropriate conduits and the spool valve 202 to the track drive motor 32 thereby driving the-motor 32 in a forward direction. Similarly, the hydraulic fluid emanating from the second power outlet 184 flows through appropriate conduits and the spool valve 204 to the track drive motor 38 thereby driving the motor 38 in the forward directron.

Since the rates of flow of hydraulic fluid exiting from the first and second power outlets 182 and 184 of the flow compensator 176 are equal, the respective track drive motors 32 and 38 are therefore driven at the same speed. It will, therefore, be readily apparent that the apparatus will then be driven alongside the string line 84 on a path parallel thereto.

If for some reason the apparatus 10 should deviate from the desired path parallel to the string line 84, the sensor control assembly 72 will sense themovement of the apparatus 10 away from or into the string line 84 and, through the sensor unit 80 and the tracer 82, the hydraulic differential flow control valve 270 will be actuated to cause automatic correction of the path of the apparatus 10 to bring it back to the desired path parallel to the string line 84. v If the apparatus 10 deviates from the desired path toward the string line 84 the deviation is sensed by the sensor control assembly 72 which causes the hydraulic differential flow control valve 270 to be actuated by the sensor unit 80-causing hydraulic fluid to emanate from the signal outlet port 276 while there is no flow of hydraulic fluid emanating from the signal outlet port 274. The hydraulic fluid exiting from the signal outlet port 276 flows through conduits 78 and 162 into the first inlet 158 and out the outlet 144 of shuttle valve 142.

The hydraulic fluid exiting from the outlet 144 flows through conduit 146 into the second signal inlet 124 of the flow divider 120.

As best shown in FIG. 3, the hydraulic fluid entering the second signal inlet 124 of the flow divider 120 flows into the annular chamber 324 formed therein and exerts hydraulic pressure on the valve member 282 thereby urging the valve member 282 to the left within the valve body 280, as viewed in FIG. 3. The hydraulic fluid within the annular chamber 324 flows therefrom through orifice 340 into chamber 352 in the valve member 282. As the hydraulic fluid flows through the orifice 340, the pressure thereof drops to that of the hydraulic fluid within the chamber 352.

Since hydraulic fluid is entering the second signal inlet 124 while there is no flow of hydraulic fluid entering the first signal inlet 122, the hydraulic pressure urging the valve member 282 to the left is greater than the hydraulic pressure urging the valve member 282 to the right. Due to this pressure differential being exerted on the valve member 282, the valve member 282 is displaced to the left an amount proportional to the differential in these two hydraulic pressures thereby overcoming, to some extent, the urging of spring assembly 358.

When the valve member 282 moves from the center position within the valve body 280 to the left, it will be displacement of the valve member 282 to the left Within the valve body 280.

As a result of the previously described displacement of the valve member 282 to the left within the valve body 280, in response to the differential hydraulic signal received from the sensor control assembly 72, the rate of flow of hydraulic fluid emanating from the third annular chamber 314 through the second power outlet 130 is proportionally greater than the rate of flow of the hydraulic fluid emanating from the second annular chamber 306 through the first power outlet 128. The stream of hydraulic fluid emanating from the second power outlet 130 flows through the flow compensator 1'76 and the spool valve 204 in the previously described conduits to the track drive motor 38 while the stream of hydraulic fluid emanating from the first power outlet 128 flows through the flow compensator 176 and the spool valve 202 and the previously described conduits to the track drive motor 32. Since the rate of flow of the stream of hydraulic fluid entering track drivemotor 38 is proportionally greater than the rate of flow of the stream of hydraulic fluid entering track drive motor 32, the speed of the track drive motor 38 is increased proportionally over the speed of the track drive motor 32 thereby causing the apparatus 10 to swing away from the string line 84 back toward its proper line of direction parallel to the string line 84.

As the apparatus 10 approaches proper alignment with the string line 84, the sensor control assembly 72 senses the approach of the apparatus 10 toward proper alignment and causes the hydraulic differential flow control valve 270 to be gradually actuated back into its neutral position so that hydraulic fluid ceases to emanate from the signal outlet port 276 thereof when the apparatus 10 is again in proper alignment with the string line 84. When hydraulic fluid flow from the control valve 270 ceases, the hydraulic pressures acting on the opposite ends of the valve member 282 of the flow divider are equal thus permitting the valve member 282 to be properly centered within the valve body 280 by the spring assembly 358. When the valve member 282 is in the center position the rates of flow of hydraulic fluid emanating from the first and second power outlets 128 and 130 of the flow divider 120 are substantially equal and the resulting speeds of the track drive motors 32 and 38 are also substantially equal.

If the apparatus 10 deviates from the desired path away from the string line 84, the deviation is sensed by the sensor control assembly 72 which causes the hydraulic differential control valve 270 to be actuated by the sensor unit 80 causing hydraulic fluid to emanate from the signal outlet port 276 while there is no flow of hydraulic fluid emanating from the signal outlet port 276. The hydraulic fluid exiting from the signal outlet port 274 flows into the first signal inlet122 of the flow divider 120 via the previously described conduits and shuttle valve. 136.

As described above, the hydraulic fluid entering the second signal inlet 124 of the flow divider 120 flows into the annular chamber 324 and exerts hydraulic pressure on the valve member 282 thereby urging the valve member 282 to the left within the valve body 280, as viewed in FIG. 3. The hydraulic fluid within the annular chamber 324 flows therefrom through orifice 340 into chamber 352 in the valve member 282. As the hydraulic fluid flows through the orifice 340 the pressure thereof drops to that of the hydraulic fluid within the chamber 352.

I Since hydraulic fluid is entering the first signal inlet 122 while there is no flow of the hydraulic fluid entering the second signal inlet 124, the hydraulic pressure urging the valve member 282 to the right is greater than the hydraulic pressure urging the valve member 282 to the left. Due to this pressure differential being exerted on the valve member 282, the valve member 282 is displaced to the right in an amount proportional to thedifferential in these two hydraulic pressures thereby overcoming, to some extent, the urging of spring assembly 358.

When the valve member 282 moves from the center position within the valve body 280 to the right, it will be readily apparent that the cross-sectional area of fluid communication between the chamber 352 and the third annular chamber 314 afforded by the ports 356 is decreased an amount proportional to the displacement of the valve member 282 to the right. Similarly, it will be also readily apparent that the cross-sectional area of fluid communication between the chamber 352 and the second annular chamber 305 afforded by the ports 352 is increased an amount proportional to the displacement of the valve member 282 to the right within the valve body 280. 7

As a result of the previously described displacement of the valve member 282 to'the right within the valve body 280, in response to the differential hydraulic signals received from the sensor control assembly 72, the rate of flow of hydraulic fluid emanating from the second annular chamber 306 through the first power outlet 128 is proportionally greater than the rate of flow of the hydraulic fluid emanating from the third annular chamber 314 through the second power outlet 130. As described above, the stream of hydraulic fluid emanating from the second power outlet 130 flows through the flow compensator 176 and the spool valve 204 to the track drive motor 38 while the stream of hydraulic fluid emanating from the first power outlet 128 flows through the flow compensator 176 and the spool valve 202 to the track drive motor 32. Since the rate of flow of the stream of hydraulic fluid entering track drive motor 32 is proportionally greater than the rate of flow of the stream of hydraulic fluid entering track drive motor 38, the speed of the track drive motor 32 is increased proportionally over the speed of track drive motor 38 thereby causing the apparatus 10 to swing back toward the string line 84 and its proper line of direction parallel to the string line 84..

As the apparatus 10 approaches proper alignment with the string line 84, the sensor control assembly 72 senses the approach of the apparatus 10 toward proper alignment and causes the hydraulic differential flow control valve 270 to be gradually actuated back into its neutral position so that hydraulic fluid ceases to emanate from the signal outlet port 274 thereof when the apparatus 10 is again in proper alignment with the string line 84. When hydraulic fluid flow from the control valve 270 ceases, the hydraulic pressures acting on the opposite ends of the valve member 282 in the flow divider are equal thus permitting the valve member 282 to be properly centered within the valve body 280 by the spring assembly 358. When the valve member 282 is in the center position the rates of flow of hydraulic fluid emanating from the first and second power outlets 128 and of the flow divider 120 are substantially equal and the resulting speeds of the track drive motors 32 and 38 are also substantially equal.

It will be readily apparent to those skilled in the art that the operation of the sensor control assembly 72 and the flow divider 120 during the forward movement of the apparatus 10 applies equally when the apparatus 10 is operated in the reverse direction. The apparatus 10 is placed in condition to operate in the reverse direction by placing the forward-reverse control valve 186' in the reverse position thereby causing the spool valves 202 and 204 to be placed in the reverse position when the pump 20 is driven by the engine through the power takeoff. Automatic correction of the path of the apparatus 10 when deviating from the proper path parallel to string line 84 is accomplished just as described above for forward operation of the apparatus 10.

When the apparatus 10 is moving in the forward -direction and is following the proper path parallel to the string line 84, it is not uncommon for the track drive motors 32 and 38 driving the apparatus 10 through the respective hydraulically driven track units 16 to encounter different loads thereby requiring greater power from one track drive motor than from the other in order for the apparatus 10 to continue along the proper path. The apparatus of the present invention provides for the automatic adjustment of the power outlets. of

the track drive motors through the'action of the flow.

compensator 176. t

As previously described above, when the apparatus 10 is properly following a path parallel to the string line 84 the flow rates of the streams of hydraulic fluid emanating from the first and second power outlets 128 and 130 of the flow divider 120 are equal. When the track drive motors 32 and 38 are each encountering the same amount of load, the streams of hydraulic fluid entering the first and second power inlets 178 and of the flow compensator 176 from the first and second power outlets 128 and 130 of the flow divider 120, are also equal. The stream of hydraulic fluid entering the first power inlet 178 flows into the chamber 446 formed in the valve member 396 through the ports 450.

Similarly, the stream of hydraulic fluid entering the second power inlet 180 flows into the chamber 448 formed in the valve member 396 through ports 452. The hydraulic fluid in the chamber 446 flows through ports 454 into the third annular chamber 424 and out therefrom through the first power outlet 182 of the flow compensator 176. The hydraulic fluid in the chamber 448 flows therefrom through the ports 456 into the fourth annular chamber 432 and out therefrom through the second power outlet 184 of the flow comfrom the second power outlet 184 flows therefrom through the spool valve 204 to the track drive motor 38 through the previously described interconnecting conduits.

If the track drive motor 32, for example, encounters a greater load than the track driver motor 38 the rate of flow of hydraulic fluid into the track drive motor 32 is reduced thus increasing the pressure of the hydraulic fluid in the conduits interconnecting the first power outlet 182 and the track drive motor 32 over the hydraulic pressure of the hydraulic fluid in the conduits interconnecting the track drive motor 38 and the second power outlet 184. The increase in hydraulic pressure at the first power outlet 182 over the hydraulic pressure at the second power outlet 184 is communicated through the ports 454 and 456 into the respective chambers 446 and 448. Since the hydraulic pressure in the chamber 446 is greater than the hydraulic pressure in the chamber 448, the valve member 396 is displaced to the right within the valve body 394 in an amount proportional to the pressure differential between the hydraulic fluid in the chamber 446 and the hydraulic fluid in the chamber 448.

As the valve member 396 is displaced to the right within the valve body 394, as viewed in FIG. 4, the cross-sectional area of fluid communication between the chamber 446 and the third annular chamber 424 afforded by the ports 454 is increased while the crosssectional area of fluid communication between the chamber 448 and the fourth annular chamber 432 afforded by the ports 456 is decreased. The maximum displacement of the valve member 396 to the right within the valve body 394 is mechanically limited by the abutment of the end face 444 of the valve member 396 with the end plate 460. It should be noted that when the end face 444 abuts the end plate 460, fluid communication between the chamber 448 and the fourth annular chamber 432 through the ports 456 is preferably completely eliminated.

It will be readily apparent that displacement of the valve member 396 to the right within the valve body 394 will decrease the cross-sectional area of fluid communication between the second power inlet 180 and the second power outlet 184 and simultaneously increase the cross-sectional area of fluid communication between the first power inlet 178 and the first power outlet 182. In efiect, a dummy load is introduced between the second power inlet 180 and the second power outlet 184 which results insubstantially equal hydraulic pressure drops between the first power inlet 178 and the first power ouetlet 182, and between the second power inlet 180 and the second power outlet 184. Thus, the hydraulic fluid streams emanating from the first and second power outlets 128 and 130 of the flow divider 120 will encounter substantially equal loads regardless of the loads encountered by the track drive motors 32 and 38.

On the other hand, if the track drive motor 38 encountersa greater load than that encountered by the track drive motor 32, the pressure of the hydraulic fluid communicating between the chamber 448 and the track drive motor 38 will be increased proportionally over the pressure of the hydraulic fluid communicating between the chamber 446 and the track drive motor 32. This differential in hydraulic pressure causes the displacement of the valve member 396 to the left within the valve body 394 in an amount proportional to the pressure differential between the hydraulic fluid in the chamber 448 and the hydraulic fluid in the chamber 446.

As the valve member 396 is displaced to the left in the valve body 394, as viewed in FIG. 4, the crosssectional area of fluid communication between the chamber 448 and the fourth annular chamber 432 afforded by the ports 456 is increased while the crosssectional area of fluid communication between the chamber 446 and the third annular chamber 424 is decreased. The maximum displacement of the valve member 396 to the left within the valve body 394 is mechanically limited by abutment of the end face 442 of the valve member 396 with the end plate 458. It should be noted that when the end face 442 abuts the end plate 458, fluid communication between the chamber 446 and the third annular chamber 424 through the ports 454 is preferably completely eliminated.

It will be readily apparent that the displacement of the valve member 396 to the left within the valve body 394 will increase a cross-sectional area of fluid communication between the second power inlet 180 and the second power outlet 184 and simultaneously decrease the cross-sectional area of fluid communication between the first power inlet 178 and the first power outlet 182. In effect, as noted above, a dummy load is introduced between the first power inlet 178 and the first power outlet 182 which results again in substantially equal hydraulic pressure drops between the first power inlet 178 and the first power outlet 182, and between the second power inlet 180 and the second power outlet 184. Thus, again, the hydraulic fluid streams emanating from the first and second power outlets 128 and 130 of the flow divider 120 will continue to encounter substantially equal loads regardless of the loads encountered by the track drive motors 32 and 38.

It should also be noted that the operation of the flow compensator 176 when the apparatus 10 is in proper condition to move inthe reverse direction is identical to that previously described. The displacement of the valve member 396 in either direction within the valve body 394 in response to load variations encountered by the track drive motors 32 and 38 is proportional to the differential between the respective loads encountered thereby. It will be readily apparent that as the differential between the loads encountered by the track drive motors continually increases or decreases, the resulting displacement of the valve member 396 within the valve body 394 continuously controls the hydraulic pressure drops between the first power inlet 178 and first power outlet 182, and between the second power inlet 180 and second power outlet 184, thus maintaining these hydraulic pressure drops substantially equal regardless of the loads encountered by the track drive motors 32 and 38.

It should also be noted that provision has been made for manually overriding the automatic control of the apparatus 10 by the automatic control assembly 18 by means of the hydraulic manual steering control assembly 64. The hydraulic manual steering control assembly 64 also provides the primary means of steering the apparatus 10 when the shut-off valve 86 is placed in the closed position thereby deactivating the previously described sensor control assembly 72.

If the shut-off valve 86 is in the closed position with the sensor control assembly 72 deactivated, and the operator desires to steer the forwardly moving apparatus to the right, the operator moves the control lever 268 in the direction R asshown in FIG. 2. The movement of the control lever 268 in the direction R causes the hydraulic .fluid entering the hydraulic differential flow control valve 260 through the inlet port 262 to emanate from the signal outlet 266 in a stream having a greater flow rate than the stream of hydraulic fluid emanating from the signal outlet 264. The differential in the flow rates of the hydraulic fluid streams emanating from the signal outlets 266 and 264 is proportional to the magnitude of the movement of the control lever 268 by the operator. The stream of hydraulic fluid emanating from the signal outlet 266 flows through the previously described conduits to the shuttle valve 142 and from the shuttle valve 142 through the conduit 146 to the annular chamber 324 of the flow divider 120. The stream of hydraulic fluid emanating from the signal outlet 264 flows through the previously described conduits to shuttle. valve 136 and from shuttle valve 136 7 through conduit 140 to the annular chamber 322 of the flow divider120.

As described in detail above for the automatic operation of the automatic control assembly 18, the difference in the hydraulic pressures acting on the opposite ends of the valve member 282 causes the displacement thereof to the left, as viewed in FIG. 3, within the valve body 280 and results in a proportionally greater flow of hydraulic fluid to the track drive motor 38 than the flow rate of hydraulic fluid to the track drive motor 32 thereby increasing the speed of the track drive motor 38 over the speed of the track drive motor 32 and causing theapparatus 10 to swing to the right.

It will be readily apparent to those skilled in the art that the movement by the operator of the control lever 268 in the direction L, as shown in FIG. 2, will cause displacement of the valve member 282 to the right within the valve body 280 of the flow divider 120, thereby causing the track drive motor 32 to operate at a speed greater than that of the track drive motor 38 thereby causing the apparatus 10 to swing to the left.

The operation of the hydraulic manual steering control assembly 64 when used to override the control signals of the sensor control assembly 72 is identical to that described in detail above. Assuming the shut-off valve 86 is in the open position and the sensor control assembly 72 is activated, it will be readily apparent to those skilled in the art that if the flow rate of hydraulic fluid emanating from the signal outlet 264 of the by draulic steering control assembly 64 is greater than the flow rate of the hydraulic fluid emanating from the signal outlet 274 of the sensor control assembly 72, the shuttle valve 136 will check the flow of hydraulic fluid entering the first inlet 148 thereof thereby allowing the hydraulic fluid entering the second inlet 150 to pass into the check valve and out through the outlet 138 to flow to the flow divider 120 through conduit 140. Similarly, if the flow rate of hydraulic fluid emanating from the signal outlet 266 of the hydraulic manual steering control assembly 64 is greater than the flow rate of hydraulic fluid emanating from the signal outlet port 276 of the sensor control assembly 72, the shuttle valve 142 will act to close the first inlet 158 thereof and open the second inlet 160 thereof, thereby passing hydraulic fluid into the check valve 142 to exit from the outlet 144 thereof and flow to the flow divider 120 through conduit 146.

It should be noted that when the sensor control as- I sembly 72 is deactivated by placing the shut-01f valve 86 in the closed position, the shuttle valves 1'36 and 142 will operate to close the respective inlets 148 and 158 thereof. It should also be noted that when the sen sor control assembly 72 is activated by placing the shutoff valve 86 in the open position and when the hydraulic manual steering control assembly 64 is in the neutral position, the shuttle valves 136 and 142 will operate to close the respective inlets 150 and 160 thereof.

DESCRIPTION OF THE EMBODIMENTS OF FIGS.

7 5, 6, 7 AND 8 FIG. 5 generally illustrates, in schematic form, a slightly modified automatic control assembly 18a in fluid communication with the hydraulic manual steernot illustrated in FIG. 5 for the same reason as explained in the discussion of the automatic control assembly 18 above.

The automatic control assembly 18a comprises a bidirectional differential valve 500. The bi-directional differential valve 500 includes a first inlet-outlet port 502, a second inlet-outlet port 504, a high pressure outlet port 506 and a low pressure return port 508. The first inlet-outlet port 502 is in fluid communication with the first port 20a of the track drive pump 20 via conduits 118 and 22.

The automatic control assembly 18a also includes a slightly modified flow divider 120a having first and second signal inlets 122 and 124, a power inlet 126 and first and second power outlets 128 and 130. The power inlet 126 of the flow divider 120a is in fluid communication with the second inlet-outlet port 504 of the differential valve 500 via conduit 134.

A shuttle valve 136 having an outlet 138 is in fluid communication with the first signal inlet 122 of the flow divider 120a via conduit 140. A second shuttle valve 142 having an outlet 144 is in fluid communication with the second signal inlet 124 of the flow divider 120a via conduit 146. Y

The shuttle valve 136 further includes a first inlet 148 and a second inlet 150. The first inlet 148 is influid communication with the sensor control assembly 72 via conduits 152 and 76. The second inlet is in fluid communication with the hydraulic manual steering control assembly 64 via conduits 154, 156 and 68.

The second shuttle valve 142 further includes a first inlet 158 and a second inlet 160. The first inlet 158 is in fluid communication with the sensor control assembly 72 via conduits 162 and 78. The second inlet is in fluid communication with the hydraulic manual steering control assembly 64 via conduits 164, 166 and 70.

The second inlet 150 of the shuttle valve 136 is also in fluid communication with the low pressure return port 508 of the bi-directional differentialvalve 500 via conduits 154, 510 and 512 with an orifice S14 interposed in conduit 510 intermediate conduits 154 and 512. The second inlet 160 of the shuttle valve 142 is also in fluid communication with the low pressure return port 508 of the bi-directional differential valve 500 via conduits 164, 516 and 512 with an orifice 51,8

interposed in conduit 516 intermediate conduits 164 and 512.

The outlet 138 of shuttle valve 136 is in fluid communication with the low-pressure return port 508 of the bi-directional differential valve- 500 via conduits 140, 520 and 512 with an orifice 522 interposed in conduit 520 intermediate conduits 140 and 512. The outlet 144 of shuttle valve 142 is also in fluid communication with the low pressure return port 508 of the bi-directional differential valve 500 via conduits 146, 524 and 512 with an orifice 526 interposed in conduit 524 intermediate conduits 146 and 512.

The automatic control assembly 18a further includes a slightly modified flow compensator 176a. The flow compensator 176a includes first and second power inlets I78 and 180, and first and second power outlets 182 and 184. The flow compensator 176a further includes first and second reverse-compensation inlets 528 and 530.

The hydraulic manual steering control assembly 64 preferably includes a conventional hydraulic differential flow control valve 260, described above, having an inlet port 262 and a pair of signal outlet ports 264 and 266. The valve 260 may be suitably actuated by a manually operated control lever or the like as shown at 268. The inlet port 262 of the control valve 260 is in fluid communication with the high pressure outlet port 506 of the bi-directional differential valve 500 via conduits 66, 532 and 534. The signal outlet 264 is in fluid communication with the conduit 68 and the signal outlet 266 is in fluid communication with the conduit 70.

The sensor control assemblyv 72 includes a conventional hydraulic differential flow control valve 270, described above, having an inlet port 272 and a pair of signal outlet ports 274 and 276. The signal outlet port 274 is in fluid communication with conduit 76 and the signal outlet port 276 is in fluid communication with conduit 78. The inlet port 272 is in fluid communication with the high pressure outlet port 506 of the bidirectional differential valve 500 via conduits 74, 536 and 534. As described above, a shut-off valve 86 is installed in the conduit 74 intermediate the inlet port 272 of the sensor control assembly 72 and the automatic control assembly 18a. The hydraulic differential flow control valve 270 is of conventional construction and its operation will be readily the art.

The sensor unit 80 is operatively connected to the hydraulic differential flow control valve 270 of the sensor control assembly 72 for actuation of the valve 270 in response to variation in the position of the sensor unit 80 relative to the string line 84. The sensor unit 80 may be directly connected to the valve 272 by mechanical means or may be connected electrically to the valve 272 to provide actuation thereof. Such sensor units are well-known in the art and need not be described in detail herein.

The automatic control assembly 18a further includes a hydraulically actuated selector spool valve 538 having first and second control ports 540 and 542, first and second inlets 544 and 546, and first and second outlets 548 and 550. The first control port 540 is in fluid communication with the first inlet-outlet port 502 of the bidirectional differential valve 500 via circuits 552 and 118. The second control port 542 is in fluid communication with the second port 20b of the track drive pump 20 via conduits 554, 556 and 24. The second control apparent to those skilled in port 542 is also in fluid communication with the track drive motor 32 via conduits 554, 558, 44 and 46. The second control port 542 is further in fluid communication with the track drive motor 38 via conduits 554, 560, 56 and 62.

The first port 32a of the track drive motor 32 isvin fluid communication with the first power outlet 182 of the flow compensator 176a via conduits 40, 42 and 562. The first port 380 of the track drive motor 38 is in fluid communication with the second power outlet 184 of the flow compensator 176a via conduits 52, 60 and 564.

The first power outlet 128 of the flow divider a is in fluid communication with the first power inlet 178 of the flow compensator 176a via conduit 566. The first inlet 544 of the selector valve 538 is in fluid communication with the first power outlet 128 of the flow divider 120a via conduits 568 and 566. The second power outlet 130 of the flow divider 120a is in fluid communication with the second power inlet of the flow compensator 176a via conduit 570, The second inlet 546 of the selector valve 538 is in fluid communication with the second poweroutlet 130 of the flow divider 120a via conduits 572 and 570.

As shown in FIG. 6, the flow divider 120a comprises a valve body 280 and a slightly modified valve member 282a slidingly disposed therein. The valve body 280 is identical to the valve body 280 described above for the flow divider 120 and therefore will not be described in detail again. The valve member 282a is substantially identical to the previously described valve member 282 of the flow divider 120 and the same reference characters will be used to designate those portions of the valve member 282 which are unchanged therefrom.

The cylindrically shaped outer periphery 326 of the valve member 282a has a diameter sized to provide a substantially fluid-tight seal between the outer periphery 326 and the walls of the bore 284 through the valve body 280. A cylindrically shaped extension 328 is formed on one end portion 329 of the valve member 282a and extends into the annular chamber 324 of the valve body 280. The extension 328 is coaxial with the outer periphery 326 of the valve member 282a. An annular shoulder 330 interconnects the cylindrical surface 332 of the extension 328 and the cylindrically shaped outer periphery 326. v

A bore 336a is formed in the valve member 282a intersecting the end portion 338 thereof. The bore 336a extends only partially through the valve member 282a thereby forming a chamber 352a therein. A slightly modified plug 344a having no aperture formed therein a threadedly secured in the bore 3360 at the end portion 338 of the valve member 282a. I

Two ports 350 are formed in the valve member 282a providing communication between the chamber 352a formed therein and the central annular chamber 298 of the valve body 280.

A plurality of ports 354 are formed in the valve member 282a proximate to the end portion 338 thereof. The ports 354 provide fluid communication between the chamber 352a and the outer periphery 326 of the valve member 282a. Similarly, a plurality of ports 356 are formed in the valve member 282a proximate to the end portion 329 thereof. The ports 356 provide fluid com munication between the chamber 352a and the outer periphery 326 of the valve member 282a. Preferably,

the valve member 282a includes 10 ports 354 and 10 ports 356. The arrangement of the ports 354 and 356 in the valvemember 282a is identical to the arrangement previously described for the valve member 282 andjwill not be described in detail again. It should be noted that the valve member 282a is positioned in its center or medial position within the valve body 280 as shown in FIG. 6.

As will be readily apparent to those skilled in the art, as the valve member 2820 moves either left or right of the central or medial position, the cross-sectional area of ports 354 and 356 providing fluid communication between the chamber 352a and the outer periphery 326 of the valve member 282a always remains equal to the total cross-sectional area of ports.

The valve member 282a is urged into its central or medial position relative to the valve body 280, as

shown in FIG. 6, by means of the spring assembly 358 described in detail above. The spring assembly 358 is retained on the cylindrically shaped extension 328 by means of a snap ring 372disposed in'an annular groove 374 formed in the cylindrical surface 332 of the extension 328. The previously described annular sleeve 378 is disposed within the annular chamber 324 of the valve body 280 with the first end face 380 thereof abutting the spring assembly 358 and with the second end face 382 thereof abutting the end plate 386. I

F IG. 7 illustrates a slightly modified flow compensator 176a comprising a slightly modified valve body 3940 and a slightly modified valve member 396a slidably disposed therein. Since the slightly modified flow compensator 176a is identical in many respects to the previously described flow compensator 176, like elements will be identified by the same reference characters used previously.

The slightly modified valve body 394a differs from the previously described valve body 394 only in the addition of the first and second reverse compensation inlets 528 and 530 which provide fluid communication between the exterior of the valve body 394a and the bore 398 extending through the valve body 394a.

The valve member 396a is slidably disposed in the bore 398 of the valve body 394a. The cylindrically shaped outer periphery 440a of the'valve member 396a has a diameter sized to provide a substantially fluidtight seal between the outer periphery 440a and the walls of the bore 398. The valve member 396a includes opposite end faces 442a and 4440, each lyingin a plane normal to the longitudinal axis of the valve member 396a. A cylindrically shaped chamber 446a is formed in one end of the valve member 396a with one end thereof intersecting end face 442a. A counterbore 574 is formed in the chamber 446a intersecting the end face 4420. A second cylindrically shaped chamber 448a is formed in the opposite end of the valve member 396a with one end thereof intersecting the end face 444a. A counterbore 576 is formed in the chamber 448a intersecting the end face 4440. It should be noted that the chambers 446a and 448a do not communicate with each other within the valve member 396a.

First and second circumferential grooves 578 and 580 are formed in the medial portion of the valve member 396a.-The circumferential grooves 578 and 580 communicate respectively with the first and second reverse compensation inlets 528 and 530 of the valve body 394a. Each groove 578 and 580 is of sufficient width to provide full fluid communication with the respective inlets528 and 530 throughout the full range of displacements of the valve member 396a within the valve body 394a;

A first transverse bore 582 extends transversely through the valve member 396a communicating at each end thereof with the first circumferential groove 578. The bore 582 intersects the previously described bore 4460 providing fluid communication between the first reverse compensation inlet 528 of the valve body 294a and the end face 4420 of the valve member 396a. A second transverse bore 584 extends transversely through the valve member 396a with its opposite ends intersecting the second circumferential groove 580. The bore 582 intersects the cylindrical chamber 448a thereby providing fluid communication between the second reverse compensation inlet '530 of the'valve body 394a and the end face 444a of the valve member 396a.

First and second longitudinal groove 586 and 588 are formed in the cylindrically shaped outer periphery 440a of the valve member 396a. The grooves 586 and 588 provide fiuid communication between the first annular chamber 408 and the third annular chamber 424 of the valve body 394a. The longitudinal groove 586 includes a first end wall 590 and a second end wall 592. The second longitudinal groove 588 includes a first end wall 594 and a second end wall 596. While the grooves 586 and 588 are preferred other forms of passages, such as an annular groove or the like, may be substituted therefor.

Third and fourth longitudinal grooves 598 and 600 are formed in the cylindrically shaped outer periphery 440a of the valve member 396a. The longitudinal grooves 598 and 600 provide fluid communication between the second annular chamber 416 and the fourth annular chamber 432 of the valve body 394a. The longitudinal groove 598 includes a first end wall 602 and a second end wall 604. The longitudinal groove 600 includes a first end wall 606 and a second end wall 608. While the grooves 598 and 600 are preferred, other forms of passages, such as an annular. groove or the like, may be substituted therefor.

The valve member 396a is of such length that when it is displaced to the left, as viewed in FIG. 7, with the end face 442a thereof abutting the end plate 458, the cross-sectional area of fluid communication between the annular chambers 408 and 424 of the valve body 394a is closed off entirely by the respective end walls 590 and 594 of the grooves 586 and 588. Alternately, when the valve member 396a is displaced to the extreme right, as viewed in FIG. 7, with the end face 444a thereof abutting the end plate 460, the cross-sectional area of fluid communication between the annular chambers 416 and 432 of the valve body 394a is closed off entirely by the respective end walls 602 and 606 of the grooves 598 and 600. It should be noted that regardless of the relative position of the valve member 396a within the valve body 394a the cross-sectional area of fluid communication between the grooves 586 and 588 and the annular chamber 424 will preferably be equal to or greater than the crosssectional area of fluid communication between the grooves 586 and 588 and the annular chamber 408. Similarly, the crosssectional area of fluid communication between the grooves 598 and 600 and the annular chamber 432 will preferably be equal to or greater than the crosssectional area of fluid communication between the grooves 598 and 600 and the annular chamber 416.

It should be noted that the previously described flow divider 120a and the flow compensator 176a may be advantageously housed in a single unitary valve body. Such a valve body would include all of the features described for the valve bodies 280 and 3940 of the flow divider 120a and flow compensator 1760, respectively, and would place the first and second power outlets 128 and 130 of the flow divider 120a in fluid communication with the first and second power inlets 178 and 180, respectively, of the flow compensator 176a within the combined valve body. Furthermore, the end plates 458 and 384 may be advantageously combined into one end plate as may the end plates 460 and 386. In either of the described configurations the functions of the flow divider 120a and the flow compensator 176a would be identical.

As shown in FIG. 8, the bi-directional differential valve 500 comprises a valve body 610 and a valve member 612 slidably disposed therein. The valve body 610 includes a bore 614 extending therethrough and intersecting the opposite end of portions 616 and 618 thereof.

A counterbore 620 is formed in the bore 614 intersecting the end portion 616 and forming an annular wall 622 therein. A second counterbore 624 is formed in the bore 614 intersecting the opposite end portion 618 of the valve body 610 and forming an annular wall 626 therein.

The counterbore 620 forms a first annular chamber 628 within the valve body 610 adjacent the end portion 616 thereof. The counterbore 624 forms a second annular chamber 630 within the valve body 610 adjacent the end portion 618 thereof.

A third annular chamber 632 is formed in the valve body 610 coaxial with the bore 614 and includes opposite annular walls 634 and 636 interconnected by a cylindrically shaped annular surface 638. A fourth annular chamber 640 is formed in the valve body 610 coaxial with the bore 614 therethrough and includes opposite annular walls 642 and 644 interconnected by a cylindrically shaped annular surface 646.

The previously mentioned high pressure outlet port 506 communicates with the bore 614 intermediate the third and fourth annular chambers 632 and 640 thereby providing fluid communication between the bore 614 and the exterior of the valve body 610. A threaded plug 648 is threadedly secured in the counterbore 620. The threaded plug 648 includes an aperture 650 formed therein coaxial with the bore 614 and pro viding the previously described firstinlet-outlet port 502 of the valve 500. The plug 648 further includes an inwardly facing annular end face 652 formed thereon. A second threaded plug 654, identical to the threaded plug 648, is threadedly secured in the counterbore 624 of the valve body 610. The aperture 650 formed in the plug 654 provides the previously mentioned second inlet-outlet port 504 of the valve 500. The plug 654 also includes an inwardly facing annular end face 652 formed thereon.

The valve member 612 includes a cylindrically shaped outer periphery 656 and opposite end portions 658 and 660. A first circumferential groove 662 is formed in the outer periphery 656 of the valve member 612 and includes opposite annular walls 664 and 666 interconnected by a cylindrically shaped circumferential surface 668. A second circumferential groove 670 is formed in the outer periphery 656 of the valve member 612 and includes opposite annular walls 672 and 674 interconnected by a cylindrically shaped circum- .ferential surface 676.

The valve member 612 further includes opposite blind bores 678 and 680 formed therein coaxial with the axis of the valve member 612. A first counterbore 682 is formed in the blind bore 678 and a second counterbore 684 is formed in the blind bore 680. The bore 678 and the counterbore 682 formed therein form a chamber 686 in the valve member 612. Similarly, the bore 680 and the counterbore 684 formed therein form a chamber 688 in the valve member 612.

A pair of ports 690 provide fluid communication between the bore 678 and the cylindrically shaped circumferential surface 668 of the valve member 612. A pair of ports 692 provide fluid communication between the bore 680 and the cylindrically shaped circumferential surface 676 of the valve member 612.

The valve member 612 is yieldably urged into its normal, centered position, as shown in FIG. 8, by means of a pair of coil compression springs 694 and 695 disposed respectively in the counterbores 682 and 684 of the valve member 612. Each coil spring 694 and 695 is secured at the end thereof opposite the valve member 612 in an annular spring seat 696 having an L- shaped cross-section. The spring seats 696 bear respectively against the end faces 652 of the threaded plugs 648 and 654.

The previously described low pressure return port 508 is in fluid communication with the bore 614 through the valve body 610 via passageways 698 and 700 formed in the valve body 610. The passageway 698 communicates with the bore 614 intermediate the first annular chamber 628 and the third annular chamber 632 formed in the valve body 610. The passageway 700 communicates with the bore 614 intermediate the second annular chamber 630 and the fourth annular chamber 640 formed 'in the valve body 610;

OPERATION OF THE EMBODIMENT OF FIGS. 5, 6, 7 AND 8 In operation, the track drive pump 20 is driven by the engine and power take-off (not shown) to provide a source of pressurized hydraulic fluid. The pressurized. hydraulic fluid provided by the pump 20 may be in either a low pressure range of from 600 to 1500 psi or in a high pressure range of from 1,500 to 3,500 psi. While these pressure ranges are disclosed as preferable for the operation of this embodiment of the present invention, it is not intended that the present invention be limited thereby.

Forward and reverse operation of the apparatus 10 is provided by alternately driving the track drive pump 20 in what will be called the forward direction or, alternately, driving the pump 20 in the reverse direction. This particular mode of operation is contrasted with the previously described mode of operation wherein 

1. A bi-directional differential valve for use in an automatic control system of a hydraulic drive system comprising: a valve body having an exterior surface and a bore extending therethrough and intersecting the opposite end portions thereof; a valve member, having a substantially cylindrically shaped outer periphery and opposite end portions, slidably disposed within the bore through said valve body; a first inlet-outlet port formed in one end portion of said valve body and communicating between the bore and the exterior surface thereof; a second inlet-outlet port formed in the opposite end portion of said valve body and communicating between the bore and the exterior surface thereof; a high-pressure outlet port formed in said valve body and communicating between the medial portion of the bore and the exterior surface thereof; a first annular chamber formed in said valve body coaxial with the bore therethrough, said first annular chamber being disposed intermediate said high-pressure outlet port and one end portion of said valve body and proximate to said highpressure outlet port; a second annular chamber formed in said valve body coaxial with the bore therethrough, said second annular chamber being disposed intermediate said high-pressure outlet port and the opposite end portion of said valve body and proximate to said high-pressure outlet port; a low-pressure return port formed in said valve body and communicating with the exterior surface thereof; a first passageway formed in said valve body communicating between said low-pressure outlet port and the bore, said first passageway communicating with the bore intermediate said first annular chamber and one end portion of said valve body; a second passageway formed in said valve body communicating between said low-pressure return port and the bore, said second passageway communicating between the bore intermediate said second annular chamber and the opposite end portion of said valve body; a first chamber formed in one end portion of said valve member; a second chamber formed in the opposite end portion of said valve member; a first circumferential groove formed in the outer periphery of said valve member adjacent to said first annular chamber; a second circumferential groove formed in the outer periphery of said valve member adjacent to said second annular chamber; a first port formed in said valve member and communicating between said first circumferential groove and said first chamber thereof; a second port formed in said valve member and communicating between said second circumferential groove and said second chamber thereof; and biasing means carried by said valve body and operatively engaging said valve member for yieldably urging said valve member into a center position within the bore of said valve body and being adapted to permit sliding movement of said valve member within the bore, overcoming the urging of said biasing means, toward the first end portion or alternately, toward the opposite end portion of said valve body in response to the pressure of fluid entering said second inlet-outlet port or, alternately, entering said first inlet-outlet port, respectively.
 2. A bi-directional differential valve as defined in claim 23 wherein said biasing means is characterized further to include: a first spring disposed in the bore of said valve body intermediate said valve member and one end portion of said valve body; and a second spring disposed in the bore of said valve body intermediate said valve member and the opposite end portion of said valve body. 